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JavaScript html5 canvas Draws the clock effect

  • 2021-01-18 06:16:07
  • OfStack

This article illustrates JavaScript+html5 canvas drawing clock effect. To share with you for your reference, as follows:

HTML parts: 


<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, initial-scale=1.0,minimum-scale=1.0,maximum-scale=1.0">
 <title>canvas drawing </title>
</head>
<body onload="init()">
<canvas id="canvas" width="200px" height="200px"></canvas>
</body>
</html>

JavaScript parts: 


function init(){
 var canvas = document.getElementById("canvas"),
  context = canvas.getContext("2d");

 setInterval(function(){draw(canvas, context)},1000);
}
function draw(canvas, context){
 var x = canvas.width,
  y = canvas.height,
  r = Math.min(x/2, y/2);

 context.clearRect(0, 0, x, y); // Clear painting history 
 // Painting clock box 
 context.fillStyle = "#f1f1f1";
 drawCircle(context, x, y, r);
 // Painting language 
 var tx = x/2,ty = y/2,tr = 0.8*r;
 context.font = "bold 12px  Microsoft jas black ";
 context.fillStyle = "#000";
 drawText(context, "1", tx + 0.5*tr,ty - 0.866*tr);
 drawText(context, "2", tx + 0.866*tr, ty - 0.5*tr);
 drawText(context, "3", tx + tr, ty);
 drawText(context, "4", tx + 0.866*tr, ty + 0.5*tr);
 drawText(context, "5", tx + 0.5*tr, ty + 0.866*tr);
 drawText(context, "6", tx, ty + tr);
 drawText(context, "7", tx - 0.5*tr, ty + 0.866*tr);
 drawText(context, "8", tx - 0.866*tr, ty + 0.5*tr);
 drawText(context, "9", tx - tr, ty);
 drawText(context, "10", tx - 0.866*tr, ty - 0.5*tr);
 drawText(context, "11", tx - 0.5*tr, ty - 0.866*tr);
 drawText(context, "12", tx, ty - tr);
 // Get the current time 
 var date = new Date(),
  h = date.getHours(),
  m = date.getMinutes(),
  s = date.getSeconds(),
  angleH = (360/12)*Math.PI/180,
  angleM = (360/60)*Math.PI/180
 context.strokeSyle = "#000";
  // Degree of plotting time 
  drawScale(context, x, y, r, angleH, -0.88*r, -0.96*r, 3);
  // Drawing fractional scale 
  drawScale(context, x, y, r, angleM, -0.93*r, -0.96*r, 1);
 // The second hand of a painting 
 drawCircle(context, x, y, 3);
 drawNeedle(context, x, y, r, h*angleH + m*angleM/12, -0.5*r);
 drawNeedle(context, x, y, r, m*angleM + s*angleM/60, -0.6*r);
 drawNeedle(context, x, y, r, s*angleM, -0.75*r);

}
// Painting circle 
function drawCircle(context, x, y, r){
 context.save();
 context.beginPath();
 context.arc(x/2, y/2, r, 0, Math.PI*2, 0);
 context.fill();
 context.closePath();
 context.restore();
}
// 4) painting text method 
function drawText(context, text, x, y){
 context.save();
 x -= (context.measureText(text).width/2);
 y += 4;
 context.translate(x, y);
 context.fillText(text, 0, 0);
 context.restore();
}
// Scale drawing method 
function drawScale(context, x, y, r, rotate, start, end, lineWidth){
 context.save();
 context.beginPath();
 context.translate(x/2,y/2);
 context.lineWidth = lineWidth;
 for (var i = 0; i < 60; i++) { 
  context.rotate(rotate);
  context.moveTo(0, start); 
  context.lineTo(0, end);
 }
 context.closePath();
 context.stroke();
 context.restore();
}
// The second hand method of painting 
function drawNeedle(context, x, y, r, rotate, line){
 context.save();
 context.translate(x/2,y/2);
 context.beginPath();
 context.rotate(rotate);
 context.moveTo(0, 0.1*r);
 context.lineTo(0, line);
 context.closePath();
 context.stroke();
 context.restore();
}

I hope this article is helpful to JavaScript program design.

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